Nice write up! I was in almost the same boat as you. I had an 08 civic Si that I traded for the WRX. I hated the 6 speed in the civic though. It wasn't geared like a true 6 speed. In the civic I would shift into 6th in the same spot I shift the WRX into 5th. It felt like just another gear to shift into that yielded no power. The VTEC hit hard but i feel that my WRX spools up quicker than I could get into VTEC.
I admit, acceleration the WRX has the edge BUT not by much(stock). With just a few modes though the WRX can't be touched by a K20.
The BIG difference to me is on the interstate. Going 70-80 on the interstate and coming up behind a slow truck I would need to almost down shift in the civic to get the power to blow past but in the WRX its a simple move of the big toe and i'm gone. And like you said, the K20 is to expensive to mod